The present invention relates to rechargeable, secondary batteries comprising a lithium manganese oxide as the positive electrode. More particularly, the invention provides a method for the low temperature synthesis of lithium manganese oxides of the formula Li.sub.1+x Mn.sub.2 O.sub.4 where x ranges from 0 to 1.
Lithium manganese oxides have proven particularly useful as positive intercalation electrode materials in secondary batteries comprising negative electrodes of intercalatable materials, such as carbon in the form of graphite or petroleum coke, in lieu of potentially hazardous free lithium metal. Such a battery is in the discharged state when assembled, since only upon being charged does the negative electrode intercalate lithium ions from the positive electrode. During subsequent discharge of the battery, the lithium ions return to the positive electrode where they remain intercalated until the charging step of the next cycle. This shuttling of the lithium ions between electrodes during the charge-discharge cycling has led to the concept of the "rocking chair" battery.
Due to the loss of intercalatable lithium ions in certain irreversible secondary reactions, particularly during the first charging cycle, an excess of lithium is required in these cells in order to maintain a useful energy level. An immediate solution to this problem is to include an excess of lithium source positive electrode material. This expedient results in a significant loss of cell capacity, however. The more desirable alternative is to use as the positive electrode a compound which contains a greater amount of lithium per unit formula, thus offering a larger lithium reservoir without affecting cell capacity. The present invention provides a convenient method for the relatively low temperature synthesis of high quality lithium manganese oxides containing up to about two atoms of lithium per unit formula. When used as positive electrodes in "rocking chair", type secondary cells, these materials can double the cell capacity and yield increased energy density.